Identifying mine tailings risks and rewards

It is no secret that mining produces waste that can be damaging to the environment, but with advances in technology and knowledge, the ability to reduce the environmental impacts of mine tailings improves. The use of x-ray diffraction (XRD) and fluorescence (XRF) enables environmental scientists to not only identify potential risks in mine tailings but also offer advice on the potential for re-processing.

Tasmania’s historic gold and copper mines are notorious for the damage that waste has caused to the environment, to the point where in one particular region the damage itself was a tourist attraction. The visible signs of damage are the red stains, waste rock and tailing heaps that surround the mine, all of which can affect the water supply and river systems through leaching and run-off.

Almost all of these mine sites contain sulfide minerals (such as pyrite), which are oxidised under weathering conditions producing acid. This mine waste can have devastating effects on the environment, which can be costly to clean up, but may be a lucrative source for re-processing as older mining techniques left much of the mineral resources behind.

To quantify the potential re-processing value or the extent to which mine tailing remediation is needed requires extensive testing of the waste material. In the past, samples would be gathered and sent to laboratories – the results could be several weeks before they are known and costly for the company.

According to Dr Dane Burkett, Applications and Marketing Manager, Olympus, “Portable XRD (pXRD) and portable XRF (pXRF) analysers provide users with mineralogy and geochemistry onsite, in near real time. This allows the user to make more informed decisions onsite and can significantly reduce the number of samples which are sent offsite for analysis by other more costly, analytical techniques. Our pXRD analysers are capable of identifying and quantifying all minerals, irrespective of reflectance and our pXRF analysers are capable of providing fast, accurate and repeatable geochemical results, onsite.”

The Olympus TERRA pXRD and Vanta pXRF units have enabled Dr Anita Parbhakar-Fox, Senior Research Fellow in Geoenvironmental Studies with the ARC Transforming the Mining Value Chain Research Hub, University of Tasmania to identify and quantify the sulfide, carbonate and clay mineralogy, and characterise the geochemistry, onsite. With this information Dr Parbhakar-Fox is able to determine the acid forming potential at a given site as well as the ability of the carbonate and clay minerals to naturally buffer the system. She is also able to use these portable devices as a screening tool for determining which samples merit further analysis by more expensive laboratory analytical methods. Moreover, as a lecturer, it has given her the ability to give onsite education to students on field trips to understand what they are visually witnessing.

“When you are in the field it can be frustrating not having a clear idea of what the samples contain,” said Dr Parbhakar-Fox. “A basic understanding of the geochemistry provided by the Vanta pXRF goes a long way, but does not reveal the types of sulfide minerals present or how metal transfers may occur. Using the Olympus TERRA pXRD in conjunction with the pXRF you have a greater idea of what is going on and it saves having to take a sample back to the lab”.

“A recent field trip with undergraduate students to an old gold mine on Tasmania’s east coast showed that the tailings had a high sulfide – pyrite – content, the host for the gold and with modern extraction technology could be worth re-processing. It also highlights the potential for further acid rock drainage. Being able to determine the carbonate and clay mineralogy within the tailings – both qualitatively and quantitatively with pXRD – also allowed the students to assess the ability of the tailings to naturally buffer the acidity caused by oxidation of sulphides.”

“The accuracy and convenience of the Olympus equipment means that preliminary reports can be given to show where the variations in sulfides, carbonates and clays are in gold mine tailings and recommendations or further testing can be done with a higher degree of confidence; this equipment gives an excellent first pass indication,” said Dr Parbhakar-Fox

The portable Olympus Vanta pXRF and TERRA pXRD analysers only require small samples, 5g and 15mg, respectively. The Vanta provides quantification of elements Mg to U on the periodic table, while the TERRA provides quantitative mineralogical analysis across all mineral species.

Both units are designed for field usage and consequently are battery operated and built to withstand rugged environments and given high IP ratings. Data and preliminary reports can be stored within the unit or transmitted via Bluetooth connectivity to mineralogy experts or clients.

Dr Parbhakar-Fox adds that for students, the theoretical knowledge becomes meaningful once they are in the field to gain understanding of what is happening in the real world and believes it would be fantastic if more students and professionals were able to use the Olympus analysers to fully appreciate the potential and toxicity of mine tailings.